1. Field of the Invention
The present invention relates to a method for forming a self-aligned contact hole. More particularly, the present invention relates to a method for forming contact holes between closely disposed conductive structures on a substrate using a self-aligning process.
2. Description of the Related Art
As semiconductor devices become more highly integrated and are required to have higher response speeds, patterns formed on a substrate must become increasingly minute. More particularly, a width of a pattern and a space between adjacent patterns are being greatly reduced. Specifically, since a contact should be formed to connect isolated devices on a semiconductor substrate to a highly conductive film, while an aligning margin and an isolation margin are maintained, the contact occupies a significant area on the semiconductor substrate. Accordingly, dimensions of the contact greatly affect the overall size of a memory device in which identical cells are repeatedly formed, such as a dynamic random access memory (DRAM), a static random access memory (SRAM) or a non-volatile memory (NVM).
Recently, a contact having a minute size has not been able to be exactly formed using conventional semiconductor manufacturing methods even though the semiconductor technology has been rapidly developed to form a line width of below approximately 0.25 xcexcm. In addition, heights of conductive film patterns have increased in order to reduce resistances of the conductive film patterns as widths of the conductive film patterns have decreased. As a result, formation of a contact between the conductive film patterns becomes increasingly difficult. Hence, in a case that a design rule does not have a sufficient margin and patterns having identical shapes are repeatedly formed, such as in a memory device, a method for forming a contact hole using a self-aligning process has been developed to reduce the overall area of the device.
FIGS. 1A to 1E illustrate cross-sectional views of stages in a conventional method for forming a self-aligned contact hole.
Referring to FIG. 1A, after a conductive film is formed on a substrate 10, a nitride film is formed on the conductive film. Then, portions of the nitride film and the conductive film are etched to expose the substrate 10 so that conductive structures 15 including conductive film patterns 12 and nitride film patterns 14 are formed on the substrate 10.
Referring to FIG. 1B, a nitride film is uniformly formed on the conductive structures 15 and on the substrate 10. The nitride film is then anisotropically etched so that the nitride film remains at sidewall portions of the conductive structures 15, thereby forming nitride spacers 16. Here, upper portions of the nitride film patterns 14 on the conductive film patterns 12 are partially etched while the nitride film on the substrate 10 is completely removed. Thus, the upper portions of the nitride film patterns 14a have rounded shapes.
Referring to FIG. 1C, an insulation film 18 including silicon oxide is formed to fill a space between the conductive structures 15 including the nitride spacers 16.
Referring to FIG. 1D, using an anisotropic etching process having an etching selectivity between silicon oxide and silicon nitride, a predetermined portion of the insulation film 18 is etched to form a preliminary contact hole exposing a portion of the substrate 10 between the conductive structures 15 including the nitride spacers 16a. When the insulation film 18 is etched to expose the portion of the substrate 10 between the conductive structures 15 having the nitride spacers 16, an upper portion of the nitride spacers 16a is etched in accordance with a ratio corresponding to the etching selectivity.
Referring to FIG. 1E, the substrate 10 and the resultant structures formed thereon are rinsed with a rinsing chemical to remove polymers generated during the etching so that self-aligned contact holes 20 are formed. When the substrate 10 is rinsed, an exposed portion of the etched insulation film 18a is partially etched.
As the patterns become much smaller to meet demand of high integration of semiconductor devices, several disadvantages of this conventional method for forming the self-aligned contact hole become apparent.
First, a thickness of the nitride spacer 16 should be reduced so that a space between the conductive structures 15 may be significantly decreased. When the nitride spacer 16 has a relatively large thickness, the space between the conductive structures 15 becomes so narrow that the insulation film 18 may not be able to completely fill in the space. In addition, a parasitic capacitance may be increased due to the nitride spacer 16. Alternately, when the thickness of the nitride spacer 16 decreases, the conductive film pattern 12 covered by the nitride spacer 16 may be easily exposed because the nitride spacer 16 may be consumed during formation of the self-aligned contact hole 20. As a result, a bridge failure frequently occurs between the conductive film pattern 12 and conductive materials filling the self-aligned contact hole 20.
Second, upper side, or xe2x80x9cshoulder,xe2x80x9d portions of the nitride spacers 16a become increasingly rounded as widths of the conductive structures 15 decrease. When the shoulder portions of the nitride spacers 16a have more rounded shapes, predetermined portions of the nitride spacers 16 and the nitride film patterns 14a are rapidly etched during the formation of the self-aligned contact hole 20, so the conductive film patterns 12 covered by the nitride spacers 16 may be exposed.
Third, a depth of the contact hole 20 necessarily increases as the heights of the conductive structures 15 increase. Thus, a process failure such as a non-opening of a contact may increase.
Fourth, a remaining portion of the etched insulation film 18a on the nitride spacer 16 significantly decreases as the space between adjacent conductive structures 15 decreases. Further, the remaining portion of the etched insulation film 18a may be completely removed during subsequent processes. Hence, a process failure frequently occurs wherein the conductive materials filling the contact holes 20 are connected to each other during the subsequent processes.
The present invention has been made in an effort to solve the aforementioned problems and accordingly, it is a feature of an embodiment of the present invention to provide a method of forming a self-aligned contact hole that is able to minimize process failures.
In order to provide this feature of an embodiment of the present invention, there is provided a method for forming a self-aligned contact hole including (a) forming a plurality of conductive structures on a semiconductor substrate, each conductive structure including a conductive film pattern having an upper and side surfaces and a protection pattern formed on the upper and surfaces of the conductive film pattern; (b) forming a first insulation film to fill a space between adjacent conductive structures; (c) successively etching upper portions of the first insulation film and the protection patterns until each of the protection patterns has a level upper surface that is exposed; (d) forming a second insulation film on the resultant structure on the semiconductor substrate; and (e) selectively etching portions of the second insulation film and the first insulation film using a photolithography process to form the self-aligned contact hole exposing a portion of the semiconductor substrate between adjacent conductive structures.
In one embodiment of the present invention, the successive etching results in the first insulation film being etched slower than the protection pattern so that a portion of the first insulation film filled between adjacent conductive structures protrudes from the upper surface of the conductive structures.
The method of the present invention may further include forming a nitride liner on the plurality of conductive structures and on the semiconductor substrate after forming the plurality of conductive structures. In addition, the method preferably includes forming a conductive material in the self-aligned contact hole to form a contact.
According to the present invention, a process failure, such as a non-opening of the contact, may be prevented because protection patterns have level upper surfaces, and the protection patterns have heights lower than conventional protection patterns. In addition, consumption of the protection patterns may be reduced during etching to form a contact hole because an etching selectivity between the protection pattern and the first and second insulation films is enhanced.